Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $41.27   6.199%   $43.8283   $43.83   $43.85   $43.80  
  Purchase #2 $95.72   7.562%   $102.9583   $102.96   $102.95   $103.00  
  Purchase #3 $23.74   4.109%   $24.7155   $24.72   $24.70   $24.70  
  Purchase #4 $223.51   7.842%   $241.0377   $241.04   $241.05   $241.00  
  Purchase #5 $49.30   5.474%   $51.9987   $52.00   $52.00   $52.00  
  Purchase #6 $48.88   10.184%   $53.8579   $53.86   $53.85   $53.90  
  Purchase #7 $188.93   3.115%   $194.8152   $194.82   $194.80   $194.80  
  7 purchase totals = $671.35       $713.2116   $713.23   $713.20   $713.20